Phase I will involve extensive research experience and graduate level coursework in molecular genetics and immunology at Harvard, MIT, and Woods Hole. Research in Dr. Beverley's laboratory will focus upon elucidating the molecular mechanisms of resistance to antifolate drugs in the pathogenic protozoan Leishmania major. Beverley and his colleagues have developed lines of L. major resistant to the antifolate agent methotrexate (MTX). They have shown that MTX resistance involves the amplification of at least two segments of the genome, one of which includes the gene encoding the bifunctional enzyme dihydrofolate reductase/thymidylate synthetase, which is the target of the drug. This system will provide the opportunity to learn the techniques of recombinant DNA analysis, cloning, and enzyme kinetics, and will serve as a useful paradigm for the study of drug resistance in general. During Phase II, the approaches learned in Phase I will be applied, at the Infectious Diseases Unit of MGH, to studying folate metabolism and its inhibition in the related protozoan Trypanosoma cruzi. This topic has scarcely been studied. Given the remarkable productivity of antifolate research in other fields including chemotherapy against cancers, bacteria as well as other parasites, this would appear to be an important area to pursue. A long-term goal of this work will be to apply insights gained at the molecular level toward developing effective agents against this dreaded pathogen.